The present invention relates to an improved receiver unit for use in a low voltage line conductor probe system.
Wiring systems comprising various cables and service lines exist in the interior of building structures such as, for example, plants and offices. Usually, service lines are branched off at different locations from the main line where panel boards are normally provided. Each panel board has a plurality of circuit breakers disposed therein. A main switch is inserted between the plurality of circuit breakers and low voltage service lines.
In performing the service of certain existing low voltage lines or the installation of additional receptacles to such lines, it is highly required that such low voltage service lines be disconnected from the main line for safety reasons. However, it is very difficult to determine which of circuit breakers in the panel board is electrically associated with the low voltage line to be serviced. One approach to solving this problem is to open the main switch to render all the associated lines conductors "dead". However, this results in shutting off of all electrical apparatus such as computers connected to the main switch. Accordingly, it is necessary to disconnect only the low voltage line conductors to be serviced while keeping the other lines live.
Japanese Laid Open Patent Application No. 62-261075 discloses a probe system for use with a multiple-conductor cable, which basically comprises a probe signal transmitter, a probe signal receiver including a probe coil and a display unit. The probe coil is in the form of a ring having one portion cut away to enable insertion of a conductor under test through the ring. In use of this probe system, the transmitter is connected to one end of the conductor to supply a probe signal thereto. The receiver is positioned at the other end of the cable in such a manner that the probe coil may detect the magnetic flux induced by the probe signal through the conductor.
The present invention contemplates the use of this prior art concept to determine which of circuit breakers in a panel board is electrically associated with a specific line conductor or conductors. Typically, the panel board has a protective insulating cover having openings through which operating knobs extend outwardly. The operating knobs are operatively associated with their respective circuit breakers in the panel board. In trying to determine which of the circuit breakers in the panel board is electrically associated with a particular line conductor, the line conductor is supplied with an electrical current having a predetermined frequency through a receptacle, while the panel board is probed for the magnetic flux generated by the current, by use of a flux detecting coil. During the probing operation, the protective insulating cover must not be removed from the remaining structure of the panel board to eliminate the possibility of accidental contact with energized portions in the panel board.
In case of such low voltage line conductor probing applications, it should be noted that the magnetic flux generated by the current flowing in the circuit breakers has a pattern which is different from that generated by the current through the multiple-conductor cable as described above. Each of the circuit breakers in the panel board has a pair of spaced conductors extending in parallel to each other, and the direction of AC current flowing through the spaced conductors is opposite to each other. In this arrangement, the direction of the magnetic flux generated around one of the conductors is different from that of the magnetic flux generated around the other conductor, as is well known to those skilled in the art. The magnetic flux generated by both conductors in an area located therebetween is oriented generally perpendicular to a "reference" plane in which both conductors lie. Accordingly, it should be understood that a simple application of the above-described prior art concept to this particular case will not provide an effective and efficient method of detection, since if the coil is positioned outside the protective insulating cover at a point midway between the conductors in parallel to the reference plane, the coil will produce no voltage signal. Thus, it is impossible to determine which of the circuit breakers in the panel board is electrically associated with the low voltage line conductors.
It is, accordingly, an object of the invention to provide a receiver unit for use in a low voltage line conductor probe system which can produce a peak voltage when the receiver unit is positioned on a panel board in alignment with the circuit breaker in the panel board that is electrically associated with a particular low voltage line conductor.